A process of pretreatment of metal-plating a resin molded article molded from a resin composition containing as main components a polyphenylene sulfide (PPS) resin, a glass-reinforcing agent and optionally one or more other thermoplastic resins comprises(1) treating the resin molded article by immersion in an oxidative acid solution (A treatment),(2) treatng the resulting resin molded article by immersion in an organic polar solvent-containing liquid (B treatment), and then(3) treating the resulting resin molded article by immersion in a solvent which can dissolve one or both of the glass reinforcing agent and one or more of the other thermoplastic resins (C treatment). The PPS resin contains a paraphenylene sulfide unit ##STR1## in an amount of at least 70 mole % of all recurring units. Total amount of PPS resin and the glass-reinforcing agent is at least 60% by weight of the resin composition, and the ratio of the PPS resin to the glass-reinforcing agent is in the range of 2:8 to 9:1 by weight. The other thermoplastic resin, preferably polyester, polyarylate, polyamide, polyetherimide, polyethersulfone and polycarbonate is contained in an amount of 5 to 20% by weight. Typically the acid solution used in A treatment is a mixed liquid of hydrogen peroxide and sulfuric acid, and the organic polar solvent-containing liquid used in C treatment contains N-methylpyrrolidone or dimethylacetamide in an amount of at least 5% by weight. C treatment includes sulfuric acid treatment (C-1 treatment) and/or aqueous alkali solution treatment (C-2 treatment).